The present invention relates to paper machines.
In particular, the present invention relates to a machine especially adapted for manufacturing a paper such as tissue paper. The web-forming part of the machine includes a web-carrying means in the form of a wire or felt on which pulp stock is supplied from a headbox. The path taken by the web-carrying means is determined by guide means which influence the dewatering action and which in addition provide for the web-carrying means a reversal in its direction of travel. A web-pressing means cooperates with the web-carrying means to form a twin-wire type of construction therewith, the web-pressing means also taking the form of a suitable wire or felt and the latter having with the web-carrying means a common path of travel over a substantial portion of the path taken by the web-carrying means at the region where the path of travel of the latter is reversed.
It is known to manufacture paper such as tissue paper by forming the web on a comparatively short wire section which resembles a normal planar wire with the headbox supplying the stock onto a breast roll which frequently has a suitably recessed surface or which communicates with an internal source of vacuum, with the web travelling, while supported by the wire, past conventional dewatering elements such as table rolls, deflectors, foil strips, suction boxes and a suction roll, each of which serves to remove water from the stock web, although structures of this latter type have been omitted in certain instances with relatively new designs. After web formation has progressed to a certain degree, the partly dried web is transferred to a pick-up felt or the like, and while supported by the latter the web is subjected to further drying in the press and drying sections of the machine.
In order to simplify the machine and reduce the amount of space occupied thereby, in some designs the planar wire section has been omitted. With such a construction the formation of the web takes place on a breast roll which is totally wire-covered and from which the web is directly transferred to a pick-up felt.
In recent years there has been developed so-called twin-wire formers wherein formation of the paper web takes place between a pair of wires, in a manner differing from web formation by way of a Fourdrinier wire section. As a result of the efficient dewatering action achieved with twin-wire formers, the wire portion of the structure can be made much shorter and in many respects is more economical than a conventional Fourdrinier wire arrangement. However, twin-wire formers of this latter type have a serious drawback in that the stock is usually supplied into the throat formed between the wires as they converge toward each other. With this latter construction the stock is immediately subjected to a voilent dewatering action with this intense dewatering taking place simultaneously in a pair of opposed directions, through both wires, during formation of the web. Along with the violent extraction of water, large amounts of fine fibers and fillers also tend to escape, with the result that the web loses its softness and resilience. Inasmuch as these latter properties are important for tissue paper, these twin-wire formers have proved to be unsuitable for the manufacture of paper of this type.